Viral infections commonly trigger the transcription of antiviral genes, including type 1 interferon (IFN). Newly produced IFNs are released from the cell, and activate a signal transduction cascade that induces the transcription of many interferon responsive genes whose products set up an antiviral state in uninfected neighboring cells. Many viruses have evolved to counteract this host defense mechanism, allowing virus replication to occur. The overall focus of this research is to investigate the balance between the ability of the host to induce the antiviral IFN response, and the ability of vesicular stomatitis virus (VSV) to block induction of this system. The cytotoxic VSV matrix (M) protein inhibits host-directed transcription and limits IFN gene expression in VSV-infected cells. The goal of this project is to determine if M protein is solely responsible for suppression of IFN gene expression based on its ability to inhibit host transcription, or if there is a specific mechanism by which VSV regulates IFN gene expression. Our preliminary data suggest that the later is true. We've demonstrated that NF-kappaB activation, an upstream activator of IFN gene expression, is regulated differently in cells infected with an IFN-inducing and IFN-suppressing strains of VSV. We propose that a second viral function inhibits NF-kappaB activation. This viral component would therefore play a crucial role in induction of IFN gene expression. To test this hypothesis, the specific aims to be addressed are: (1) To characterize the VSV Indiana Hr genes from an IFN-suppressing and IFN-inducing strain of VSV by cloning and determining the sequence of each viral gene. (2) To identify the viral component responsible for activation of NF-kappaB, we will investigate NF-kappaB activation in cells infected with recombinant M-defective strains of VSV, as well as determining if activation of NF-kappaB is suppressed in cells transfected with an expression vector encoding one of the viral genes. (3) To understand the mechanism by which the virus regulates NF-kappaB activation, we will determine if IkappaB has been degraded and investigate the phosphorylation status of the IkappaB Kinase in VSV-infected and transfected cells. Upon completion of this project, we will gain new insights into virus modulation of the host interferon response. Detailed knowledge of this cellular response to viral infection could be useful to the development of new antiviral and anticancer therapies.